Three hours earlier, an insurgent mortar attack near the same Kadhimiya mosque killed seven people and wounded 36 others.

Government officials are investigating that attack and the stampede. They said they also want to explore the extent of any "technical defects" on the bridge.

"This will leave a scar in our souls and will be remembered with those who died in the result of terror acts," President Jalal Talabani said.

The scale of the tragedy shocked the nation, prompting comparisons to stampedes at other religious events, such as those in Mecca during the annual Hajj pilgrimage in Saudi Arabia.

Wednesday's ceremony is one that annually attracts millions of Shiite pilgrims to Baghdad.

The Shiite faithful converge on the Kadhimiya mosque to commemorate the martyrdom of Imam Moussa al-Khadhem, a prominent figure in Shiite history buried there.

Security had been tight at the bridge, with barricades and searches adding to the congestion.

The bridge across the Tigris leads to the shrine and is an important juncture in Baghdad -- separating Kadhimiya from Adhamiya, a longtime insurgent stronghold with a strong Sunni Arab presence.

Al-Jaafari gave a nationally televised address about the stampede and earlier mortar attack in an attempt to calm Iraqis.

He urged people "to be patient with the current circumstances" and called on the country's Shiites, Sunnis and Christians "to think about the benefit of Iraq."

"We heard the news that some of those enemies attacked innocent people with mortars killing our faithful sons. This attack caused chaos among the Iraqi people in other areas in Baghdad and then because of the technical defects of the bridge, many people were martyred."

Other developments

U.S. Marine planes pounded what officials described Thursday as "an identified terrorist safe haven" in the western Anbar province near the Syrian border. The 2nd Marine Division said that F/A 18s obliterated a building in Husayba with precision-guided, 500-pound bombs, adding that the number killed in the airstrikes was undetermined.

The Iraqi government on Thursday hanged three people convicted of murder and rape, according to Laith Kubba, a spokesman for the prime minister's office. The hangings marked the first time since the toppling of Saddam Hussein's regime in 2003 that such executions had been carried out. (Full story)